Encapsulated miniature hard disc drive

ABSTRACT

The present invention is directed to a miniature hard disc drive having a metal base plate, an actuator assembly wherein the actuator assembly comprises a plurality of bearings, a shaft, and a housing; a spindle motor assembly comprising a stator with conductors, a shaft, a plurality of bearings, and a rotor; and a monolithic body of phase change material unitizing said actuator assembly housing and stator to the base plate. Methods of developing and constructing the hard disc drive are also disclosed.

FIELD OF THE INVENTION

[0001] The present invention relates generally to a hard disc drive. Itrelates particularly to a miniature hard disc drive that uses a highspeed spindle motor assembly, an actuator assembly and to theconstruction and arrangement of the spindle motor assembly and actuatorassembly to align and retain the respective component parts of theassemblies, as well as motor and other component assemblies used in theminiature hard disc drive, and methods of manufacturing hard discdrives.

BACKGROUND OF THE INVENTION

[0002] Computers commonly use disc drives for memory storage purposes.Disc drives include a stack of one or more magnetic discs that rotateand are accessed using a head or read-write transducer. Miniature harddisc drives are smaller than other hard disc drives and are used inhand-held electronic devices and portable electronic devices such ascellular phones, hand-held personal computers, digital cameras andpersonal digital assistants (PDA's). Typically, a high-speed motor suchas a spindle motor is used to rotate the discs. An example of aminiature hard disc drive is International Business Machines' (IBM)Microdrive™.

[0003] An example of a conventional spindle motor 1 used in a hard discdrive is shown in FIG. 1. The motor 1 includes a base 2 which is usuallymade from die cast aluminum, a stator 4, a shaft 6, bearings 7 and adisc support member 8, also referred to as a hub. A magnet 3 and fluxreturn ring 5 are attached to the disc support member 8. The stator 4 isseparated from the base 2 using an insulator (not shown) and attached tothe base 2 using a glue. Distinct structures are formed in the base 2and the disc support member 8 to accommodate the bearings 7. One end ofthe shaft 6 is inserted into the bearing 7 positioned in the base 2 andthe other end of the shaft 6 is placed in the bearing 7 located in thehub 8. A separate electrical connector 9 may also be inserted into thebase 2.

[0004] Each of these parts must be fixed at predefined tolerances withrespect to one another. Accuracy in these tolerances can significantlyenhance motor performance.

[0005] In operation, the disc stack is placed upon the hub. The statorwindings are selectively energized and interact with the permanentmagnet to cause a defined rotation of the hub. As hub 8 rotates, thehead (not shown) engages in reading or writing activities based uponinstructions from the CPU in the computer.

[0006] Manufacturers of disc drives are constantly seeking to improvethe speed with which data can be accessed. To an extent, this speeddepends upon the speed of the spindle motor, as existingmagneto-resistive head technology is capable of accessing data at a rategreater than the speed offered by the highest speed spindle motorcurrently in production. The speed of the spindle motor is dependentupon the dimensional consistency or tolerances between the variouscomponents of the motor. Greater dimensional consistency betweencomponents leads to a smaller gap between the stator 4 and the magnet 3,producing more force, which provides more torque and enables fasteracceleration and higher rotational speeds. One drawback of conventionalspindle motors is that a number of separate parts are required to fixmotor components to one another. This can lead to stack up toleranceswhich reduce the overall dimensional consistency between the components.Stack up tolerances refers to the sum of the variation of all thetolerances of all the parts, as well as the overall tolerance thatrelates to the alignment of the parts relative to one another.

[0007] An important characteristic of a hard drive is the amount ofinformation that can be stored on a disc. One method to store moreinformation on a disc is to place data tracks more closely together.Presently this spacing between portions of information is limited due tovibrations occurring during the operation of the motor. These vibrationscan be caused when the stator windings are energized, which results invibrations of a particular frequency. These vibrations also occur fromharmonic oscillations in the hub and discs during rotation, causedprimarily by non-uniform size media discs.

[0008] An important factor in motor design is the lowering of theoperating temperature of the motor. Increased motor temperature affectsthe electrical efficiency of the motor and bearing life. As temperatureincreases, resistive loses in wire increase, thereby reducing totalmotor power. Furthermore, the Arhennius equation predicts that thefailure rate of an electrical device is exponentially related to itsoperating temperature. The frictional heat generated by bearingsincreases with speed. Also, as bearings get hot they expand, and thebearing cages get stressed and may deflect, causing non-uniform rotationand the resultant further heat increase, non-uniform rotation requiringgreater spacing in data tracks, and reduced bearing life. One drawbackwith existing motor designs is their limited effective dissipation ofthe heat, and difficulty in incorporating heat sinks to aid in heatdissipation. In addition, in current motors the operating temperaturesgenerally increase as the size of the motor is decreased.

[0009] Manufacturers have established strict requirements on theoutgassing of materials that are used inside a hard disc drive. Theserequirements are intended to reduce the emission of materials onto themagnetic media or heads during the operation of the drive. Of primaryconcern are glues used to attach components together, varnish used toinsulate wire, and epoxy used to protect steel laminations fromoxidation.

[0010] In addition to such outgassed materials, airborne particulate ina drive may lead to head damage. Also, airborne particulates in the discdrive could interfere with signal transfer between the read/write headand the media. To reduce the effects of potential airborne particulate,hard drives are manufactured to exacting clean room standards and airfilters are installed inside of the drive to reduce the contaminationlevels during operation.

[0011] With the rapidly expanding development of personal computers intothe field of first what was termed portable, then lap-top, notebook andnow hand held size computers and digital cameras, there has been atremendous demand for smaller disc drives with increased performance forsuch small computers. Especially important to manufacturers, is theability to reduce the height of the disc drive so that the size of thecasing for the computer could be minimized. It is an objective of thepresent invention to provide a compact hard disc drive system that iscompatible with notebook and hand held computer applications, and can becompatible with devices using Type I and Type II Flash memory devices.

[0012] Another objective of the invention is to provide a compact harddisc drive system that has lower vibration and greater structuralintegrity to provide increased data storage capability and increasedspeed.

[0013] Another example of a spindle motor that can be used in a harddrive is shown in U.S. Pat. No. 5,694,268 (Dunfield et al.)(incorporated herein by reference). Referring to FIGS. 7 and 8 of thispatent, a stator 200 of the spindle motor is encapsulated with anovermold 209. The overmolded stator contains openings through whichmounting pins 242 may be inserted for attaching the stator 200 to abase. U.S. Pat. No. 5,672,972 (Viskochil) (incorporated herein byreference) also discloses a spindle motor having an overmolded stator.One drawback with the overmold used in these patents is that it has adifferent coefficient of linear thermal expansion (“CLTE”) than thecorresponding metal parts to which it is attached. Another drawback withthe overmold is that it is not very effective at dissipating heat.Further, the overmolds shown in these patents are not effective indampening some vibrations generated by energizing the stator windings.

[0014] U.S. Pat. No. 5,806,169 (Trago) (incorporated herein byreference) discloses a method of fabricating an injection molded motorassembly. However, the motor disclosed in Trago is a step motor, not ahigh-speed spindle motor, and would not be used in applications such ashard disc drives. Furthermore, none of these prior art embodimentsintegrate the base of the hard disc drive, thereby eliminating the costof the base. Thus, a need exists for an improved miniature hard discdrive that is small and lightweight yet overcomes the aforementionedproblems.

BRIEF SUMMARY OF THE INVENTION

[0015] A miniature hard disc drive has been invented which overcomesmany of the foregoing problems. In addition, unique stator assembliesand other components of a high-speed motor have been invented, as wellas methods of manufacturing hard disc drives. In one aspect, theinvention is a hard disc drive having an actuator assembly that includesan actuator assembly housing; a spindle motor assembly having a statorwith conductors, a rotor, a shaft, and a plurality of bearings; a baseplate; and a monolithic body of phase change material substantiallyencapsulating said actuator assembly housing and said stator to the baseplate.

[0016] In another aspect, the invention is a miniature hard disc drivehaving a metal base plate; an actuator assembly wherein the actuatorassembly has a plurality of bearings, a shaft, and a housing; a spindlemotor assembly having a stator with conductors, a shaft, a plurality ofbearings, and a rotor; and a monolithic body of phase change materialunitizing said actuator assembly housing stator to the base plate.

[0017] In yet another aspect, the invention is a method for making aminiature hard disk drive including the steps of providing a statorhaving a plurality of poles with wire windings around said poles;providing an actuator assembly housing; providing a base plate;substantially encapsulating the stator, the actuator assembly housingand the base plate with a phase change material so as to form a unitizedbody; and forming a miniature hard disc drive from said unitized body.

[0018] The invention provides the foregoing and other features, and theadvantages of the invention will become further apparent from thefollowing detailed description of the presently preferred embodiments,read in conjunction with the accompanying drawings. The detaileddescription and drawings are merely illustrative of the invention and donot limit the scope of the invention, which is defined by the appendedclaims and equivalents thereof.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

[0019]FIG. 1 is an exploded, partial cross-sectional and perspectiveview of a conventional high-speed motor.

[0020]FIG. 2 is a top view of a hard disc drive of the present inventionwith the cover removed and showing the components encapsulated in themonolithic body with dashed lines.

[0021]FIG. 3 is a cross-sectional view of the hard disc drive of FIG. 2from a vertical cross-sectional view sectioned along a line through thespindle motor and actuator assembly axis of rotation.

[0022]FIG. 4 is a top view of a metal strip after being through theinjection molding process.

[0023]FIG. 5 is a perspective view of an injection molding process of ametal strip of the present invention.

[0024]FIG. 6 is a perspective view of a metal strip with a base plateand cover in an injection molding process of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0025] The miniature hard disc drive 10 of the present invention isshown from a top view (with the cover shell removed) in FIG. 2 and inFIG. 3 from a vertical sectional view sectioned along a line through thespindle motor and actuator assembly axes of rotation. In each of thefigures like components are designated by like reference numerals.

[0026] Referring to FIG. 3, the major elements of the miniature harddisc drive drive system 10 of the present invention are shown, includinghard disc 100, spindle motor assembly 200, and an actuator assembly 300.These components are attached to a base portion 108 of a housing. Thebase plate 108 is preferably made of stamped steel. A shell portionforms a cover 111, and in conjunction with the base portion 108,encloses the aforementioned disc drive components.

[0027] The hard disc 100 preferably has a diameter of about 27millimeters. The disc 100 has a centrally located aperture through whicha hub 102 extends. Each disc 100 is preferably constructed from glass,aluminum, or canestite having a thickness of about 0.38 millimeters andis coated with a magnetic material. Once formatted each disc is capableof having more than 2000 tracks per inch of accessible storage space.This density of tracks enables a miniature disc drive to store more than20 MB of data in a single disc system. Discs meeting these requirementsare available from Yamaha, Fuji Corporation and Hitachi Corporation, allof Japan.

[0028] The disc drive explained herein utilizes one or more magneticcoated discs 100; however, the disc drive may utilize various numbersand types of discs. For example, optical discs and associated lasertechnology based read/write heads could be used and the concepts andprinciples embodied in this invention would be fulfilled.

[0029] The means for rotatably supporting the hard disc 100 is a hub 102which is an integral part of the rotor 210 of a spindle motor assembly200. In the preferred embodiment of the present invention and asdepicted in FIG. 3, one concentrically aligned disc 100 is positioned onthe hub 102. The disc drive depicted is a single disc system; however,to increase storage capability, multi-disc systems are foreseeable.

[0030] As depicted in FIG. 3, the means for rotating the hard disc 100is preferably a spindle motor assembly 200 having an integral hub 102.The spindle motor 200 includes a stator 204, a rotor 210, a shaft 206,and bearing supports 208. The stator 204 has a plurality of poles 207with wire windings 205. Preferably each pole 207 has about 50 turns ofcopper wire 205 with an American wire gauge number of 38. The wirewindings 205 serve as conductors and induce or otherwise create aplurality of magnetic fields when electrical current is conductedthrough the conductors. In this embodiment, a magnetic field is inducedin each of the poles 207.

[0031] In the present embodiment, the integral hub 102 is fixedlymounted to a shaft 206 forming the axis of rotation of the motor 202.The shaft 206 is mounted to the base plate 108 using pins (not shown) orother conventional mounting means. Bearing supports 208 are journalledabout the shaft 206 and support a rotor 210 comprised of the hub 102 anda permanent magnet 214 positioned on a outer surface of the hub 102facing the stator 204. The interaction of a magnetic field generated bythe stator 204 with the rotor permanent magnets 214 propels the rotor210 to spin. The rotor 210, having the hub 102 as an integral component,rotates the hard disc 100. In the preferred embodiment shown in FIG. 3,there is also a base 215 that houses bearing supports 208 and shaft 206.The base 215 is not essential to practice the invention and can beremoved, and instead the hub 102 can be used to house the bearingsupports 208 and shaft 206.

[0032] The actuator assembly 300 has a voice coil motor (not shown) thatdrives an actuator arm (not shown) to pivot and swing back and forthover the disc surface 100 to read and write data. The actuator assemblyarm is attached to a shaft 306 or actuator pivot at one end. The otherend of the actuator arm has a head that reads and writes data. The shaft306 is mounted to the base plate 108 through pins or other conventionalmounting means. Bearing supports 308 are journalled about the shaft 306.The bearing supports 308 and shaft 306 are housed in a metal housing310. The metal housing 310 is preferably made of steel.

[0033] Referring to FIGS. 2 and 3, the stator 204 of the spindle motorassembly 200 and the housing 310 of the actuator assembly 300 areunitized with the base plate 108 by encapsulating them with a topsurface of base plate 108. Conventionally, the spindle motor assemblyand actuator assembly are mounted to the base using conventionalmounting features such as connecting pins or glue. In the presentembodiment, the stator 204 and the housing 310 of the actuator assembly300 and a top surface of the base plate 108 are encapsulated with aphase change material to form a unitized, preferably monolithic, body250. The phase change material used to make the body 250 is preferably athermally conductive but non-electrically conductive plastic. Inaddition, the plastic preferably includes ceramic filler particles ofeither boron nitride or preferably aluminum nitride The coefficient oflinear thermal expansion (“CLTE”) of the plastic is preferably betweenthe CLTE of steel and the CLTE of aluminum over the operatingtemperature range of the hard disc drive. A preferred form of plastic ispolyphenyl sulfide (PPS) sold under the trade name “Konduit” by LNPEngineering Plastics. Grade OTF-212-11 is particularly preferred.Examples of other suitable thermoplastic resins include, but are notlimited to, thermoplastic resins such as 6,6-polyamide, 6-polyamide, 4,6polyamide, 12,12-polyamide, and polyamides containing aromatic monomers,polybutylene terephthalate, aromatic polyesters, liquid crystalpolymers, polycyclohexane dimethylol terephthalate, copolyetheresters,polyphenylene sulfide, polyacylics, polypropylene, polyethylene,polyacetals, polymethylpentene, polyetherimides, polycarbonate,polysulfone, polyethersulfone, polyphenyloxide, polystyrene, styrenecopolymer, mixterus and graft copolymers of styrene and rubber, andglass reinforced or impact modified versions of such resins. Blends ofthese resins such as polyphenylene oxide and polyamide blends, andpolycarbonate and polybutylene terephthalate, may also be used in theinvention.

[0034] As illustrated in FIGS. 2 and 3, the body 250 encapsulates asubstantial area of a top surface of the base plate 108, stator 204, andthe external surface of actuator assembly housing 310. Afterencapsulation, the actuator assembly housing 310 and the stator 204 areunitized with base plate 108. The body 250 extends over the top surfaceof stator 204 and preferably terminates around the inner edge 211 ofstator 204. The inner side surface 212 of stator 204 is preferably leftun-encapsulated to obtain the smallest distance between the conductorsand permanent magnet 214. The inner side surface 212 may be encapsulatedwith a thin layer of phase change material without deviating from thescope of the present invention. The thickness of the body 250 may varybut is preferably at least about 0.2 millimeters. The critical thicknessrequired is that the body 250 must be thick enough so that it extendsover the top surface of stator 204. Preferably, for greater structuralintegrity the body 250 may be thicker around the edge of the base plate108.

[0035] The hard drive shown in FIGS. 2 and 3 is made in part using anencapsulation technique. This encapsulation technique involves thefollowing steps, and uses an injection mold. First, a mold isconstructed to produce a part with desired geometry. The mold has twohalves or cavities. In a preferred embodiment, the base plates arestamped into a continuous strip of metal which is fed through the mold.As shown in FIG. 4, the strip 130 creates multiple plates 108. Inalternative embodiments, the base plates 108 can be placed side by sidefor multicavity molding, or as is shown in FIG. 5 the cover can befabricated.

[0036] A preferred embodiment has the cover and base plate fabricatedside by side during molding. In this process a metal strip having both abase plate and a cover is placed in a two cavity mold. A monolithic bodyof phase change material is then injected onto the base plate and ontothe cover to form lips, grooves, and other body features. After thestrip is removed from the molding machine, and after the other internalcomponents have been added to the drive, the cover is attached to thebase plate using processes well known in the art, such as heat staking,sonic welding or glueing.

[0037] During encapsulation the base plate is placed in one half of themold and is held in place by protrusions from the mold plate whichextend through an aperture 135 in the base plate. The base plate 108,actuator assembly housing 310 and the stator 204 are aligned in positionand the two halves are closed. Plastic is injected at a pre-determinedpressure around the stator 204, actuator assembly housing 310 and baseplate 108 so as to unitize those respective parts of the hard disc driveand form the body 250 shaped as shown in FIGS. 2 and 3. Likewise plasticcan be molded around a circuit board or metal plate to form the HDDcover. After the pressure inside the mold reaches the pre-determined setpoint pressure, the phase change material is allowed to cool andsolidify. This process is repeated sequentially for the rest of the baseplates 108 if a metal strip 130 is employed.

[0038] Once the encapsulation process is complete, the other componentsof the actuator assembly and spindle motor assembly are assembledthrough conventional methods. In an alternative embodiment, it is alsocontemplated that the entire spindle motor assembly may be encapsulatedwith the actuator assembly being formed later or vice versa. It is alsocontemplated that the actuator assembly and the spindle motor assemblycan be encapsulated with the base plate. Other variations are alsocontemplated wherein at least one or more of the non-moving parts of thehard disc drive are encapsulated with the base plate. In yet anotherembodiment, it is contemplated that a base plate is injection moldedwith a layer of phase change material to form various body features suchas lips, flanges and grooves. These methods are described more fully inprovisional U.S. patent application Ser. No. 60/171,817, filed Dec. 21,1999, incorporated herein by reference.

[0039] In another preferred embodiment, the metal strip 130 hasapertures 135 which are compatible with machines that are used for othermanufacturing steps, so that the strip 130 acts as a carrier which canbe used in various manufacturing steps. By acting as a carrier, it ismeant that the metal strip 130 and the apertures 135 are configured in amanner such that the metal strip can be handled by machines, other thanan injection molding machine, that are used in the manufacturing processof a hard disc drive. As a result, using the strip 130 with apertures135 offers an easy way to manipulate small parts. Furthermore, it offersa way to ship the strips 130 to a customer for further assemblyoperations.

[0040] As illustrated in FIGS. 5 & 6, the metal strip 130 having a baseplate 108 and cover 111 may be fed continuously into an injectionmolding machine which would perform the injection molding step on eachbase plate and cover. The injection molding machine encapsulates harddisc drive components to the base plate and forms body features on thecover with a monolithic body of phase change material. The injectionmolding machine preferably performs these steps simultaneously, but itis also possible to perform them sequentially. One of ordinary skill inthe art will appreciate that it is also possible to have an injectionmolding machine with multiple cavities so that several metal strips maybe fed into the injection molding machine, thereby further increasingthe efficiency of the process. After removing the metal strip from themold, the cover may be separated from the strip or folded over andfixedly attached to the base plate.

[0041] Following the encapsulation technique in accordance with oneembodiment of the invention a hard disc drive with a thickness betweenabout two millimeters to about six millimeters may be manufactured.Preferably, in one embodiment, the disc drive would be about 3.3millimeters thick, which corresponds with a miniature disc drive used toreplace Type I flash memory devices. In another preferred embodiment, athicker disc drive with a thickness of about 5 millimeters may also bemanufactured that can be used to replace Type II flash memory devices.

[0042] Additionally, to reduce height and improve manufacturability, inone alternative embodiment, the cover 111 of the hard drive can be aprinted circuit board. Using a circuit board as a cover obviates thenecessity of having a separate cover. It is also contemplated thatplastic may be injection molded around the edges of the cover so thatthe edges of the cover and the base plate 108 are made from the samematerial. In this manner The cover may also be fixed to the base plateby methods well known in the art, such as heat staking, sonic welding orglueing.

[0043] The present invention is also directed to a method of developinga miniature hard disc drive 10. In an exemplary embodiment, the harddisc drive includes a stator having conductors and the stator issubstantially encapsulated in a body of phase change material. It hasbeen found that using this basic design concept, high-speed motors canbe developed and quickly optimized to meet various applications. Thereare several basic design parameters that can be varied when developing amotor according to the present invention: a) the composition (and thuscharacteristics) of the phase change material; b) the configuration ofthe body of phase change material; c) the magnetic design of the motor(the windings, core shape, etc.); d) the shape, size and configurationof the hub (and any discs used thereon when the motor is for a harddrive); and e) the shape, size and configuration of the actuatorassembly.

[0044] In a first embodiment, where a miniature hard disc drive isdeveloped, the method includes the following steps: a) providing anactuator assembly housing, a base plate, and a stator having multipleconductors that create a plurality of magnetic fields when electricalcurrent is conducted through the conductors, the stator and actuatorassembly housing being unitized with a base plate by substantiallyencapsulating with a body of first phase change material; b) mountingthe disc and other components of the miniature hard disc drive throughconventional means; c) energizing the actuator assembly and the spindlemotor assembly in a manner that generates vibrations, and measuring thefrequency of the vibrations; d) designing a second phase change materialthat dampens the vibrations generated by energizing the stator in stepc); and e) repeating steps a)-c), substituting the second phase changematerial for the first phase change material. At least one of the flexmodulus, elongation and surface hardness properties of the phase changematerial will be adjusted between the first and second phase changematerials to optimize vibration dampening. The phase change material ispreferably a thermoplastic. The advantages of this method of developinga hard disc drive is that the above-identified properties of the plasticmay be adjusted to meet the vibration dampening needs of a variety ofdifferent motor types and configurations. The reduced vibration willimprove motor performance and can reduce audible noise generation.

[0045] It is also possible to change the configuration of the body sothat it will result in reduced harmonic oscillations and thusvibrations. In this embodiment, the method includes the steps of and a)providing an actuator assembly housing, a base plate, and a statorhaving multiple conductors that create a plurality of magnetic fieldswhen electrical current is conducted through the conductors, the statorand actuator assembly housing being unitized with a base plate bysubstantially encapsulating with a body of first phase change material;b) mounting the disc and other components of the miniature hard discdrive through conventional means; c) energizing the actuator assemblyand the spindle motor assembly in a manner that generates vibrations,and measuring the frequency of the vibrations; d) reconfiguring theshape of the phase change material to a second configuration andrepeating steps a)-c), substituting the phase change material having thesecond configuration for the phase change material having the firstconfiguration. In this embodiment, the configuration of the body ofphase change material is adjusted to optimize vibration dampening. Ofcourse, other dimensions of body components can also be used. In thisaspect of the invention, reconfiguring the shape of the phase changematerial would also include adding such elements as a flange, grooves,etc., or even adopting a relatively different overall shape.

[0046] The present invention is also directed to an alternative methodof developing a miniature hard disc drive. Like the other methods, thismethod also involves a high-speed motor that includes a body that iscomprised of a phase change material that unitizes some components of ahard disc drive. The high-speed motor includes one or more, andgenerally a plurality of solid parts to be used in the motor either nearor within the body, such as bearings and inserts. In addition, there aresolid parts that are near the body, such as a disc support member and ahard disc drive base. The method of developing the high-speed motorcomprises designing a phase change material to have a coefficient oflinear thermal expansion such that the phase change material contractsand expands at approximately the same rate as the one or more solidparts. For example, the preferred phase change material should have aCLTE of between 70% and 130% of the CLTE of the core of the stator. Thephase change material should have a CLTE that is intermediate themaximum and minimum CLTE of the solid parts where the body is in contactwith different materials. Also, the CLTE's of the body and solid part(s)should match throughout the temperature range of the motor during itsoperation. An advantage of this method is that a more accurate tolerancemay be achieved between the body and the solid parts because the CLTE ofthe body matches the CLTE of the solid parts more closely.

[0047] Most often the solid parts will be metal, and most frequentlysteel, copper and aluminum. The solid parts could also include ceramics.In almost all motors there will be metal bearings. Thus a common elementof this aspect of the invention is developing a motor by designing thephase change material to have a CLTE approximately the same as that ofthe metal used to make the base plate 108.

[0048] Most thermoplastic materials have a relatively high CLTE. Somethermoplastic materials may have a CLTE at low temperatures that aresimilar to the CLTE of metal. However, at higher temperatures the CLTEdoes not match that of the metal. A preferred thermoplastic materialwill have a CLTE of less than 2×10⁻⁵ in/in° F., more preferably lessthan 1.5×10⁻⁵ in/in° F., throughout the expected operating temperatureof the motor, and preferably throughout the range of 0° F. to 250° F.Most preferably, the CLTE will be between about 0.8×10⁻⁵ in/in° F. andabout 1.2×10⁻⁵ in/in° F. throughout the range of 0° F. to 250° F. Whenthe measured CLTE of a material depends on the direction of measurement,thickness of the sample, or conditions of molding, the relevant CLTE forpurposes of defining the present invention is the CLTE of anencapsulated component in the direction in which the CLTE is lowest.Preferably, the CLTE in other directions is not more than 4 times thelowest value. The CLTE values are measured by a standard ASTM testmethod where the phase change material has the shape and form of themonolithic body that is overmolded on a component.

[0049] The CLTE of common solid parts used in a motor are as follows:23° C. 250° F. Steel 0.5 0.8 (× 10⁻⁵ in/in/° F.) Aluminum 0.8 1.4Ceramic 0.3 0.4

[0050] Of course, if the motor is designed with two or more differentsolids, such as steel and aluminum components, the CLTE of the phasechange material would preferably be one that was intermediate, themaximum CLTE and the minimum CLTE of the different solids, such as 0.65in/in/° F. at room temperature and 1.1×10⁻⁵ in/in/° F. at 250° F.

[0051] One preferred thermoplastic material, Konduit OTF-212-11, wasmade into a thermoplastic body and tested for its coefficient of linearthermal expansion by a standard ASTM test method. It was found to have aCLTE in the range of −30 to 30° C. of 1.09×10⁻⁵ in/in/° F. in the Xdirection and 1.26×10⁻⁵ in/in/° F. in both the Y and Z directions, and aCLTE in the range of 100 to 240° C. of 1.28×10⁻⁵ in/in/° F. in the Xdirection and 3.16×10⁻⁵ in/in/° F. in both the Y and Z directions.(Hence, the relevant CLTEs for purposes of defining the invention are1.09×10⁻⁵ in/in/° F. and 1.28×10⁻⁵ in/in/° F.) Another similar material,Konduit PDX-0-988, was found to have a CLTE in the range of −30 to 30°C. of 1.1×10⁻⁵ in/in/° F. in the X direction and 1.46×10⁻⁵ in/in/°F. inboth the Y and Z directions, and a CLTE in the range of 100 to 240° C.of 1.16×10⁻⁵ in/in/° F. in the X direction and 3.4×10⁻⁵ in/in/°F. inboth the Y and Z directions. By contrast, PPS type polymer, (Fortron4665) was likewise tested. While it had a low CLTE in the range of −30to 30° C. (1.05×10⁻⁵ in/in/°F. in the X direction and 1.33×10⁻⁵ in/in/°F. in both the Y and Z directions), it had a much higher CLTE in therange of 100 to 240° C. (1.94×10⁻⁵ in/in/° F. in the X direction and4.17×10⁻⁵ in/in/° F. in both the Y and Z directions).

[0052] In addition to having a desirable CLTE, the preferred phasechange material will also have a high thermal conductivity. A preferredthermoplastic material will have a thermal conductivity of at least 0.7watts/meter° K. using ASTM test procedure 0149 and tested at roomtemperature (23° C.).

[0053] Hard disc drives with a body of phase change materialsubstantially encapsulating the stator 204, the actuator assemblyhousing 310 and the base plate 108 wherein the phase change material hasthe CLTE or thermal conductivity as described above are themselves noveland define another aspect of the present invention. Once encapsulated,the hard disc drive will preferably be able to meet disc drivemanufacturers' industry standards for extractable particles. Using laserparticle counting, a cumulative average of particles greater than 0.5micrometers in size will total less than ten thousand particles permilliliter. This is primarily because machined mounting plates areeliminated and other sources of particulates (steel laminations, woundwire and wire/terminal connections) are sealed in the encapsulation.

[0054] Also, the encapsulation reduces outgassing because varnish usedto insulate wire in the windings and epoxy used to prevent steellaminations from oxidizing are hermetically sealed inside the statorassembly. Also, with fewer parts there is less glue needed to hold partstogether. This reduced outgassing reduces the amount of material thatcould effect the magnetic media or heads used in the disc drive.

[0055] Another aspect of the invention utilizes the basic motordescribed above that has dampened vibrations to make a hard disc drive.The dampened vibrations can be either in the audible frequency range,thus resulting in a disc drive with less audible noise, or in otherfrequencies. As mentioned earlier, the degree to which data can bepacked onto a hard drive is dependent on how close the data tracks arespaced. Due to reduced vibrations resulting from aspects of the presentinvention, the data tracks can be more closely spaced and the hard drivestill operated.

[0056] The vibrations of concern are generally produced by harmonicoscillations. The phase change material can be selected so as to dampenoscillations at the harmonic frequency generated by operation of themotor, many of which are dependent on the configuration of the windingsor other conductors. Thus, in one aspect, the invention is a motor anddisc assembly wherein the motor comprises a stator having multipleconductors that create a plurality of magnetic fields when electricalcurrent is conducted through the conductors and a monolithic body ofphase change material substantially encapsulating the conductors. Inthis respect, the phase change material has a vibration dampening effectso that the motor and disc assembly has a reduction of harmonicoscillations.

[0057] There are a number of properties of the phase change materialthat can be varied in a way that will allow the phase change material todampen different harmonic frequencies. This includes adding or varyingthe amount of glass, Kevlar, carbon or other fibers in the material;adding or varying the amount of ceramic filler in the material; changingthe type of material, such as from polyphenyl sulfide to nylon or otherliquid crystal polymers or aromatic polyesters, adding or graftingelastomers into a polymer used as the phase change material; and using adifferent molecular weight when the phase change material is a polymer.Any change that affects the flex modulus, elongation or surface hardnessproperties of the phase change material will also affect its vibrationdampening characteristics.

[0058] One way to determine the effectiveness of vibration dampening,and thus to select a suitable material, is to make up motorconfigurations where different phase change materials are used, and thenmeasure the vibration dampening accomplished by each material. Thevibration dampening can be measured with a capacitance probe or laserDoppler vibrometer. In the audible range, 20-15,000 Hz, the dampeningwill preferably be at least 2, more preferably at least 5 decibels inreduction in harmonic frequency amplitude. These reductions are assessedbased on a comparison of the vibrations of the same motor but withoutthe stator being encapsulated.

[0059] The reduced vibrations thus allow for a unique hard disc drivewith high data density and method of manufacturing the same. In thisaspect of the invention, a hard disc drive is constructed with reducedvibration characteristics. The disc drive includes a stator assembly andan actuator assembly housing that are encapsulated with the base plateto form a unitized structure with good structural properties. Thereduced vibration characteristic of the hard drive is taken advantage ofby having close data tracks on the magnetic storage media. Preferablythe data tracks are spaced so as to have at least 10,000 tracks/inch.

[0060] The vibration dampening ability of the phase change material mayalso be used in another aspect of the invention, a miniature hard discdrive having a high speed spindle motor with improved shock resistance.In this aspect of the invention, the body of phase change material isshock absorbing and thus minimizes the transfer of energy between thehousing of a hard disc drive and the magnetic storage media.

[0061] Also, with reduced vibration, there will be less friction andwear in the bearings, which results in less heat being generated by themotor, in turn resulting in longer motor and bearing life and more powerfrom the motor. Utilizing aspects of the present invention it ispossible to construct motors able to spin in hard disc drives at speedsover 5,000 rpm. A preferred motor will be able to spin at 7,500 rpm orgreater, and a more preferred embodiment will be able to spin at 10,000rpm or greater.

[0062] A number of ways to improve thermal conductivity are presented.First, the phase change material will itself provide some heatdissipation. Second, the phase change material can include additivesthat will enhance its thermal conductivity. Third, the body of phasechange material, by being in contact with a number of parts of the motorand/or disc drive, can act as a pathway for heat such that those otherparts of the motor and/or disc drive can act as heat sinks. Thisimproved thermal conductivity provides longer life to the electrical andbearing components of the motor, a higher power device, higherefficiency and lower current draw. If the motor is in a battery-powereddevice, this will extend the battery life.

[0063] Miniature hard disc drives built with the technique disclosedabove will have better reliability from lower particulate levels andreduced outgassing. The hard drives will have improved shock resistanceif the drive is dropped. The preferred motors and disc drives will havequieter operation.

[0064] The use of an encapsulated stator allows the terminal connectorsto be integrated into the body. In general, the motor can be more easilyassembled and will include fewer parts. As noted above, the stack-uptolerances are reduced because fewer components are used and the phasechange material can be designed with a CLTE that closely approximatesthat of other motor components.

[0065] It is contemplated that numerous modifications may be made to theminiature hard disc drive and method for making the miniature hard discdrive of the present invention without departing from the spirit andscope of the invention as defined in the claims. For example, while theexemplary embodiment shown in the drawings has a body 250 thatencapsulates the entire exposed top surface of base plate 108, it isconceivable that the body only encapsulates a portion of the top surfaceof the base plate so that the stator 204 and actuator assembly housing310 are unitized to the base plate 108. Furthermore, body 250 may alsoencapsulate connector pins that are inserted through the base plate 108without departing from the scope of the invention. Accordingly, whilethe present invention has been described herein in relation to severalembodiments, the foregoing disclosure is not intended or to be construedto limit the present invention or otherwise to exclude any such otherembodiments, arrangements, variations, or modifications and equivalentarrangements. Rather, the present invention is limited only by theclaims appended hereto and the equivalents thereof.

1. A hard disc drive comprising: a) an actuator pivot; b) a spindlemotor assembly comprising a stator with conductors, a rotor, a shaft,and a plurality of bearings; c) a base plate; and d) a monolithic bodyof phase change material substantially encapsulating said actuator pivotand said stator to the base plate.
 2. The hard disc drive of claim 1wherein the hard disc drive has a thickness between about 2 millimetersto about 6 millimeters.
 3. The hard disc drive of claim 1 wherein thehard disc drive has a thickness of about 3.3 millimeters.
 4. The harddisc drive of claim 1 wherein the hard disc drive has a thickness ofabout 2 millimeters.
 5. The hard disc drive of claim 1 wherein the harddisc drive has a thickness of about 5 millimeters.
 6. The hard discdrive of claim 1 wherein the hard disc drive has a disc that has adiameter of about 27 millimeters.
 7. The hard disc drive of claim 1wherein the monolithic body unitizes the stator, the actuator pivot andthe base plate together.
 8. The hard disc drive of claim 1 wherein themonolithic body unitizes the stator and the base plate together and themonolithic body unitizes the actuator pivot and base plate together. 9.The hard disc drive of claim 1 having a cover mounted to said baseplate.
 10. The hard disc drive of claim 9 wherein the cover is a printedcircuit board.
 11. The hard disc drive of claim 9 wherein the cover isovermolded with a monolithic body of phase change material.
 12. The harddisc drive of claim 1 wherein the spindle motor assembly is able tooperate over 5000 rpm.
 13. The hard disc drive of claim 1 wherein thespindle motor assembly is able to operate at at least 7500 rpm.
 14. Thehard disc drive of claim 1 wherein the spindle motor assembly is able tooperate at at least 10,000 rpm.
 15. The hard disc drive of claim 1wherein the phase change material comprises a material that changes forma liquid to a solid due to a change in temperature.
 16. The hard discdrive of claim 1 wherein the phase change material changes from a liquidto a solid due to a chemical reaction.
 17. The hard disc drive of claim1 wherein the phase change material comprises a thermosetting materialor a thermoplastic material.
 18. The hard disc drive of claim 1 whereinthe phase change material is injection molded to form the monolithicbody.
 19. The hard disc drive of claim 1 wherein the phase changematerial includes ceramic particles.
 20. The hard disc drive of claim 1wherein the phase change material has a coefficient of linear thermalexpansion of less than 2×10⁻⁵ in/in/° F. throughout the range of 0-250°F.
 21. The hard disc drive of claim 1 wherein the phase change materialhas a coefficient of linear thermal expansion of less than 1.5×10⁻⁵in/in/° F. throughout the range of 0-250° F.
 22. The hard disc drive ofclaim 1 wherein the phase change material has a coefficient of linearthermal expansion of between about 0.8×10⁻⁵ in/in/° F. and about1.3×10⁻⁵ in/in/° F. throughout the range of 0-250° F.
 23. The hard discdrive of claim 1 wherein the base comprises steel, the hub comprisingaluminum and phase change material has a coefficient of linear thermalexpansion that is between the coefficient of linear thermal expansion ofthe steel and the coefficient of linear thermal expansion of thealuminum.
 24. The hard disc drive of claim 1 wherein the phase changematerial has a thermal conductivity of at least 0.7 watts/meter° K. at23° C.
 25. The hard disc drive of claim 1 wherein the phase changematerial has a dielectric strength of at least 250 volts/mil.
 26. Thehard disc drive of claim 1 wherein the phase change material has acoefficient of linear thermal expansion in the X, Y and Z directions,wherein the coefficient of linear thermal expansion is lowest in the Xdirection, and wherein the coefficient of linear thermal expansion inthe Y and Z directions is no more than four times the coefficient oflinear thermal expansion in the X direction.
 27. A base for a minaturehard disc drive comprising: a) a metal base plate; and b) a monolithicbody layer of phase change material on one or more surfaces of the metalbase plate, wherein said monolithic body forms body features of thebase.
 28. The base of claim 27 wherein the body features compriseflanges, lips, grooves and connectors.
 29. The base of claim 27 whereinthe metal base plate comprises steel and the phase change material has acoefficient of linear thermal expansion that is between the coefficientof linear thermal expansion of the steel and the coefficient of linearthermal expansion of the aluminum.
 30. The base of claim 27 formed froma metal strip having at least two base plates.
 31. The metal strip ofclaim 30 wherein said metal strip contains apertures that allow it to beused as a carrier during the manufacturing process.
 32. The method ofclaim 27 wherein the metal strip is fed continuously through aninjection molding machine to sequentially injection mold the monolithicbody on each base plate.
 33. The hard disc drive manufactured with abase of claim 27 having a cover mounted to said base plate.
 34. The harddisc drive of claim 33 wherein the cover is a printed circuit board. 35.The hard disc drive of claim 33 wherein the cover is overmolded with amonolithic body of phase change material.
 36. A hard disc drivecomprising the base of claim 27, an actuator assembly, and a spindlemotor assembly.
 37. A miniature hard disc drive comprising: a) a metalbase plate; b) an actuator assembly wherein the actuator assemblycomprises a plurality of bearings, a shaft, and a housing; c) a spindlemotor assembly comprising a stator with conductors, a shaft, a pluralityof bearings, and a rotor; and e) a monolithic body layer of phase changematerial unitizing said actuator assembly housing and said stator to thebase plate.
 38. The miniature hard disc drive of claim 37 wherein themonolithic body layer substantially encapsulates a top surface of thebase plate, a top surface of the stator, and an external surface of theactuator assembly housing.
 39. The miniature hard disc drive of claim 37wherein the monolithic body has a thickness of about 0.2 millimeters.40. The miniature hard disc drive of claim 37 wherein the monolithicbody layer is thicker at an outer edge of the base plate.
 41. A methodfor making a miniature hard disk drive comprising: a) providing a statorhaving a plurality of poles with wire windings around said poles; b)providing an actuator assembly housing; c) providing a base plate; d)substantially encapsulating the stator, the actuator assembly housingand the base plate with a phase change material to form a unitized body;and f) forming a miniature hard disc drive from said unitized body. 42.The method of claim 41, wherein said encapsulation is performed byinjection molding in an injection molding apparatus.
 43. An electronicdevice having the miniaturized hard disc drive of claim
 37. 44. Anelectronic device having the hard disc drive of claim
 1. 45. Anelectronic device having a miniaturized hard disc drive made by themethod of claim
 41. 46. A method of manufacturing a miniature hard discdrive comprising: a) providing a metal strip having at least two baseplates; b) placing a stator on a top surface of each of said baseplates; c) injection molding a monolithic body layer of phase changematerial unitizing said stator to the base plate; d) forming a spindlemotor around the stator; and e) attaching an actuator assembly on thebase plate.
 47. The method of claim 46 wherein the metal strip is usedas a carrier.
 48. The method of claim 46 wherein the metal strip is fedcontinuously through an injection molding machine to sequentiallyinjection mold the monolithic body on each base plate.
 49. A method ofmanufacturing a miniature hard disc drive comprising: a) providing ametal base plate; b) placing a spindle motor assembly on a top surfaceof said base plate; c) injection molding a monolithic body layer ofphase change material to unitize said spindle motor assembly to the baseplate; and d) attaching an actuator assembly on the base plate.
 50. Themethod of claim 49 wherein the base plate is part of a metal strip whichcomprises at least two base plates.
 51. A method of manufacturing aminiature hard disc drive comprising: a) providing a metal base plate;b) placing an actuator assembly on a top surface of said base plate; c)injection molding a monolithic body layer of phase change materialunitizing said actuator assembly to the base plate; and d) attaching aspindle motor assembly on the base plate.
 52. The method of claim 51wherein the base plate is part of a metal strip which comprises at leasttwo base plates.
 53. A method of manufacturing a hard disc drivecomprising: a) providing a metal strip which comprises at least one baseplate and one cover; b) providing a stator assembly; c) providing anactuator assembly; d) providing a mold having two cavities; e) placingthe metal strip into the mold; and f) injection molding a phase changematerial to form a monolithic body on the base plate and cover.
 54. Themethod of claim 53 wherein the injection molding step further comprises:a) placing the stator assembly on a top surface of the base plate; andb) encapsulating said spindle motor assembly with a phase changematerial unitizing the spindle motor assembly with the base plate. 55.The method of claim 53 wherein the injection molding step furthercomprises: a) placing the actuator assembly on a top surface of the baseplate; and b) encapsulating said actuator assembly with a phase changematerial unitizing the actuator assembly with the base plate.
 56. Themethod of claim 53 wherein the metal strip is continuously fed throughthe injection molding machine to sequentially injection mold themonolithic body onto each base plate and cover.
 57. The method of claim53 wherein the metal strip comprises a predetermined number of baseplates and covers.
 58. The method of claim 53 wherein the monolithicbody forms body structures of the base and cover.
 59. The method ofclaim 58 wherein the body structures comprise flanges, lips, grooves andconnectors.